A hollow core fiber has a hollow fiber core through which light is guided. For this reason, there are no Fresnel reflections at the fiber ends, and the non-linear effects in the glass core that occur in conventional fibers are greatly reduced. The hollow fiber core is generally surrounded by further hollow areas, most of which have a smaller diameter than the fiber core, in order to maintain light guidance in the fiber core.
A very thin hollow fiber core can have a diameter of several μm to several 100 μm. In order to protect the hollow areas of such a thin hollow fiber core, a section without hollow spaces is normally spliced to fibers with hollow cores, or the end piece of the hollow core fiber is collapsed.